The present invention pertains to a lifting unit for a device for pulling monocrystals from a molten mass located in a crucible vacuum or a protective gas at reduced pressure, wherein the crucible is arranged in a vacuum chamber that is supported on a main frame and heated by the thermal radiation of a heating element, wherein a pulling shaft that makes it possible to pull the crystal up from the surface of the molten mass into a lock chamber that can be displaced relative to the main frame is provided above the molten mass, and wherein the lifting unit is held by the housing of the lock chamber, a top frame supported on the main frame or the pulling shaft.
The crystal suspended on the seedling inside the lock chamber is usually taken hold of by a special handling system that extends through a lateral opening of the lock chamber, whereafter the crystal is severed from the seedling and laterally removed from the lock chamber through the opening that can be closed by a shutter with the aid of the handling system.
This known method has a number of disadvantages, all of which result from the particular sensitivity of the crystal to shocks and vibrations. In addition, the crystal may not be properly taken hold of by the handling system because the crystal is not freely accessible while suspended in the lock chamber.
In another known device, the lock chamber is pivoted on the frame of the device together with the bulky and heavy pulling shaft and the shaft drive after the pulling process and after the ventilation of the lock chamber. In this case, the crystal can be lowered onto a transport cart that is moved underneath the lock chamber or transferred to such a transport cart. However, various devices of this type have the decisive disadvantage that the position of the individual components relative to one another cannot be ensured during the continuous operation of the system due to the size of the pulling device and the weight of its individual components. It is, in particular, very difficult to maneuver the sensitive and highly precise pulling shaft back into its proper angular position above the molten mass together with its drive.